Display devices such as television sets and movie projectors often incorporate a modulator for the purpose of distributing light into a two-dimensional pattern or image. For example, the frames of a movie reel modulate white light from a projector lamp into shapes and colors that form an image on a movie screen. In modern displays light modulators are used to turn on and off individual pixels in an image in response to electronic signals that control the modulator.
A class of MEMS light modulators was introduced in 1994 in U.S. Pat. No. 5,311,360. These devices, generally known as “grating light modulators”, modulate light by diffraction from optical gratings that are formed by mechanical ribbons. The ribbons move small distances very quickly and the gratings formed by them appear or disappear rapidly.
Approximately 250 subsequent patents refer to the '360 patent and disclose various applications, refinements and improvements to the basic grating light modulator design. Displays based on one-dimensional arrays of grating light modulators as disclosed in U.S. Pat. No. 5,982,553, for example, have met with success in the marketplace.
A new class of MEMS light modulators that incorporate ribbon structures, but use interferometric rather than diffractive optics, was introduced in 2006 in U.S. Pat. No. 7,054,051. These devices, generally known as “polarization light modulators” operate by phase shifting polarization components of light in an interferometer.
A characteristic of visual displays is contrast, or the intensity ratio of the brightest and darkest states of a display. A high contrast display can show images which contain both bright and dark pixels. Contrast improves the appearance of a display to a human observer because the human visual system can perceive variations in brightness over many orders of magnitude.
Displays incorporating MEMS light modulators sometimes encounter difficulty achieving high contrast; e.g. displaying black areas in an image. Therefore a MEMS light modulator-based display with improved contrast would be highly desirable.